A clipping path will alter the appearance of the child image by clipping the image to the coodinates specified in the path.
Examples of images with clipping paths applied.
Clippy is a good online resource to get a preset style, or create your own. You can copy the required css code from the bottom of the page.
This could be copy-pasted into the field to clip to a pentagon shape. To get a standard pentagon shape ensure the images are set to crop to square.
polygon(25% 0%, 75% 0%, 100% 50%, 75% 100%, 25% 100%, 0% 50%)
You can add a clip path via the Image Properties popup when hovering over an image.
Example of the clip path location in the Crop Image popup.